A cylindrical bearing member, which is used as sliding bearings such as a bearing body for a rotating shaft, a bushing for a chain and the like by inserting a shaft, a pin or the like into the cylindrical bore of the article, has been conventionally well known. As such, a cylindrical bearing member is well known, which is provided with a plurality of grooves, which function as oil reservoirs for a lubricating oil parallel to the axial direction of the cylindrical bearing member, that is grooves, on an inner circumferential surface of the cylindrical bearing member to enhance the lubricating properties between the inner circumferential surface in a cylindrical bore of the cylindrical bearing member, which provides a bearing surface, and a shaft, or between the cylindrical bore and a pin or the like.
In this conventional cylindrical bearing member, the grooves are extended to both ends of the cylindrical bore so that they are open on both ends of the cylindrical bore. Thus, when a shaft is inserted into the cylindrical bore of the cylindrical bearing member to use it as a bearing member while retaining a lubricating oil in the grooves, the lubricating oil flows out of open ends in the blind grooves. Accordingly, there were problems that the oil reserve efficiency is bad and when this cylindrical bearing member is used for a long period of time the lubricating properties are deteriorated.
As a bearing member, which solved such a problem, a cylindrical bearing member in which end portions of the respective grooves in the longitudinal direction of the member were blocked to form blind grooves, has been known (see Japanese Patent Publication No. 2963652)
The above-mentioned known cylindrical bearing member 21 is shown in FIG. 10. The cylindrical bearing member 21 is composed of a cylindrical portion 24, in which a rectangular crude material 22 shown in FIG. 9 was wound into a cylindrical shape, that is, a plurality of blind grooves 23 are formed by pressing, machining or rolling on a surface of the rectangular crude material 22 such as a band steel sheet, a steel sheet or the like, which provide oil reservoirs. These blind grooves 23 are blocked on the respective both ends 23a, 23a in the width direction of the crude material such as a band steel sheet. Then the cylindrical bearing member 21 is wound into a cylindrical article (cylindrical portion) by a machine so that both ends of the rectangular crude material such as the band steel sheet are opposed, and a core punch is inserted into this cylindrical article to push it into a circular shape to manufacture a round cylindrical portion 24. In the thus manufactured cylindrical bearing member 2, a seam 25 between butted portions in the rectangular crude material 22 form a groove portion.
Further, since the cylindrical bearing member 21 is formed by winding, it is a comparatively thin member. However, as another cylindrical bearing member comprising a thick cylindrical portion, a cylindrical bearing member may be used in which blind grooves for oil reservoirs were previously formed on an inner surface, that is an inner circumferential surface (bearing surface) of a cylindrical portion with a thick wall, whose outer surface was forged to a round by undercutting, broaching or the like.
Japanese Patent Publication No. 2963652 also discloses a conventional cylindrical bearing member which is formed by winding a rectangular crude material so that the ends of the rectangular crude material are in a butted state. Thus, there is a problem that this butted portion forms a seam in the width direction of the cylindrical portion. This seam provides a groove portion having no bottom. Thus there is a problem that when this cylindrical bearing member is used while inserting a shaft, a pin or the like into this cylindrical bearing member, lubricating oil in the blind grooves leaks on the side of the groove portion formed by the seam and flows out of the ends in the longitudinal direction of the seam for a very short time whereby the lubricating oil cannot be held for a long period of time and the lubricating properties cannot be maintained.
Further, there is a problem that since the cylindrical portion of this cylindrical bearing member is formed by winding a rectangular crude material, manufacturing of a cylindrical portion having a thick wall is difficult and a thick cylindrical portion cannot be formed.
Further, since in the above-mentioned conventional cylindrical bearing member comprising a cylindrical portion having a thick wall, and the blind grooves are formed on the inner circumferential surface of the cylindrical portion by undercutting, broaching or the like, the blind grooves cannot be formed by every one blind groove only, whereby the formation efficiency of the blind grooves are bad, a long time for its processing is needed and the mass production is not suitable, which leads to disadvantageous costs.